Most close by are in eyrie? (7)
I believe the answer is:
nearest
'most close' is the definition.
('near' can be a synonym of 'close')
'are in eyrie?' is the wordplay.
'in' indicates putting letters inside.
'eyrie?' becomes 'nest' (eyrie is a kind of nest).
'are' going into 'nest' is 'NEAREST'.
'by' acts as a link.
(Other definitions for nearest that I've seen before include "Most adjacent" , "touching?" , "Closest to hand" , "Sneer at (anag)" , "Stingiest" .)