transitive verb
1. : to insert or embed in (a surface)
lets in diagonal sheathing at each corner of the house
2. : to involve or commit unfavorably
the provisions … could still let us in for trouble — Elmer Davis
smiled at all her schemes, little dreaming that … she was letting him in for some £20,000 — Elizabeth Montizambert
3. : to share information with or allow to participate
learned a lot more … and I'll let you in on it — Rex Ingamells