An engagement one can look up (3)

I believe the answer is:

gig

I'm a little stuck... Click here to teach me more about this clue!

'an engagement' is the definition.
(gig is a kind of engagement)

I can't explain the remainder of the clue.

(Other definitions for gig that I've seen before include "Live performance by musicians" , "Small horse-drawn carriage" , "One-horse carriage" , "Band performance" , "One-night stand" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app