onlap1
/ˈɒnlap/Geology
noun
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.
Origin
1940s. From on- + lap, after offlap, overlap.
onlap2
/ɒnˈlap/Geology
verb
[with object] To cover (a stratum) so as to form an onlap.
Origin
1950s. From onlap.