Gas mantles oddly missing in recent delivery (7)
I believe the answer is:
neonate
'recent delivery' is the definition.
(I've seen this in another clue)
'gas mantles oddly missing' is the wordplay.
'gas' becomes 'neon' (neon is a gas).
'oddly missing' indicates alternate letters (letters in odd-numbered positions removed).
The alternate letters of 'mantles' are 'ate'.
'neon'+'ate'='NEONATE'
'in' acts as a link.
(Other definitions for neonate that I've seen before include "recently delivered" , "New-born child" , "New baby" , "One in delivery ward" , "Being recently created" .)