to extend partly under.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
How to use underlap in a sentence
The placket of a skirt should have an underlap extending well below the opening.
On the left side of the skirt sew an underlap of sufficient length to extend well below the end of the opening.
This is the type most likely either to overlap or underlap, depending upon the prison rgime and the after-parole circumstance.Criminal Types | V. M. Masten
In many cases, it is advisable to have an underlap of the material.