Definition of moult in English:


(US molt)


[no object]
  • 1(of an animal) shed old feathers, hair, or skin to make way for a new growth.

    ‘the adult birds were already moulting’
    with object ‘the snake moults its skin’
    • ‘The fall migration is preceded by a molt migration where birds molt in large groups at northern coastal sites before heading south in fresh plumage.’
    • ‘Length of the white spots, present on the tips of feathers when freshly molted, were not included in total length as in all birds these spots had worn off.’
    • ‘In general, healed injuries are considered to have resulted from trauma during molting or wounds by predatory attack.’
    • ‘In modern lobsters, the carapace material is partially resorbed prior to molting, making the carapace thin and weak.’
    • ‘This biasing factor is unique to organisms that molt or shed their skin during growth.’
    • ‘In the fall they stop over at molt sites en route to their wintering areas, where they molt and grow new feathers before they move on.’
    • ‘Because of their hard exoskeleton, to increase in size they must molt or shed their exoskeleton and produce a new one.’
    • ‘As the larva feeds and grows, it molts, shedding its cuticle.’
    • ‘Also, hermit crabs commonly kept as pets molt and shed their exoskeleton.’
    • ‘With few exceptions, only adult birds were observed to molt their flight feathers in a symmetrical pattern.’
    • ‘The larva molts again at 72 hours to become a third-stage larva.’
    • ‘These birds molt twice a year changing between alternate and basic (winter or non-breeding) plumage.’
    • ‘Unlike most birds with different breeding and non-breeding plumages, buntings molt only once a year.’
    • ‘Once animals have emerged as adults, they do not molt again, and their size and external morphology are fixed.’
    • ‘That suggests that our captive SY birds molted their juvenal flight feathers on a schedule similar to that of Tufted Puffins in the wild.’
    • ‘Each year chickens molt, often looking quite ugly, but are rewarded with new and sturdy feathers.’
    • ‘Since adult birds molt on the breeding grounds before migrating south, juveniles should be easily distinguished from adults when they first arrive in Washington in the fall.’
    • ‘The scales are shed individually, so crocodilians do not molt (shed their skin all at once) like snakes do.’
    • ‘When the lobster grows, it undergoes a process called molting, when the animal sheds its old exoskeleton and grows a new, larger one.’
    • ‘Once a year, though, when the birds molt, the tiny arthropods face life-or-death options.’
    shed, discard, slough off, throw off, get rid of, let fall, let drop
    View synonyms
    1. 1.1 (of hair or feathers) fall out to make way for new growth.
      ‘the last of his juvenile plumage had moulted’
      • ‘How often I see feathers molting to the ground-what's left of something in which nothing's to be found.’


  • A loss of feathers, hair, or skin, especially as a regular feature of an animal's life cycle.

    ‘the mountain goat is brilliant white after the autumn moult’
    ‘in the complete life cycle there are four moults’
    • ‘At concentrations of 5 ppb and above, however, the number of molts increased with an average of one third of the animals undergoing molts.’
    • ‘As suggested by Plotnick, this determination is not easily made on the basis of the fossils alone as all portions of the preservable integument may potentially be sufficiently well represented in molts.’
    • ‘The first smaller pulse induces switchover from larval to pupal commitment, and the second much larger pulse induces the pupal molt.’
    • ‘They molt twice a year, the first molt, after breeding, gives the males their eclipse plumage.’
    • ‘Occasionally, females disperse at their penultimate instar and undergo their final molt in their new webs (personal observation).’
    • ‘During each molt the animal calcifies a new carapace of about twice the volume of the previous one.’
    • ‘During the final molt, from pupa to adult, the epidermal cells secrete special enzymes that rigidify the horns as well as hardening all the other adult structures.’
    • ‘The larval stage consists of four phases, or instars, with a complete molt between each instar.’
    • ‘They noted that the cephalopod eagerly attacked the molt and invariably did so by working from the posterior of the lobster abdomen toward the anterior.’
    • ‘Second, adults and juveniles of species that mainly breed in high elevation western coniferous forests are not expected to move to the Mexican monsoon region for their fall molts.’
    • ‘One month later, lobstermen in Western Long Island Sound began to report sightings of gravid female lobsters dying in the throes of abortive molts.’
    • ‘Another subunit appears about the time of metamorphosis to first juvenile instar, and expression of a sixth subunit begins four or five molts later.’
    • ‘While all feathers wear, they are replaced regularly by the molt processes.’
    • ‘Maturation involves 7-8 molts, and molting continues into adulthood.’
    • ‘Post-embryonic development takes place during a series of four molts.’
    • ‘It is not long after this molting is complete that they start a second molt to acquire their alternate plumage.’
    • ‘Carapace width does not vary within a molt and is proportional to the length of the males' raptorial forelimbs, which they use in attacking other males.’
    • ‘The specimen also appears to be a whole animal rather than a molt: several appendages are preserved and in the first four and the last two abdominal segments a cylindrical structure is interpreted as the alimentary canal.’
    • ‘Birds eating balanced diets should have no trouble satisfying their nutritional needs during a molt.’
    • ‘The molt is restricted to replacing feathers on the head and body.’


Middle English moute, from an Old English verb based on Latin mutare ‘to change’. For the intrusive -l-, compare with words such as fault.