Oddly soppy but might watch in secret (3)
I believe the answer is:
spy
'but might watch in secret' is the definition.
I can't tell whether this definition defines the answer.
'oddly soppy' is the wordplay.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternate letters of 'soppy' are 'SPY'.
Can you help me to learn more?
(Other definitions for spy that I've seen before include "Keep watch secretly, maybe for foreign government" , "Spot" , "Glimpse" , "Discover" , "One gathers information surreptitiously" .)