Definition of onlap in US English:

onlap

noun

Geology
  • A progressive increase in the lateral extent of conformable strata in passing upwards from older to younger strata, so that each stratum is hidden by the one above; a set of strata exhibiting this.

verb

Geology
  • with object To cover (a stratum) so as to form an onlap.

Origin

1940s. From on- + lap, after offlap, overlap<br>1950s. From onlap.

Pronunciation

onlap

/ˈɒnlap/