It helps relieve congestion encountered in government holiday (7)
I believe the answer is:
menthol
'it helps relieve congestion encountered' is the definition.
The definition suggests a singular noun which matches the answer.
'in government holiday' is the wordplay.
'in' says the answer is hidden in the clue.
'MENTHOL' can be found hidden inside 'government holiday'.
Can you help me to learn more?
(Other definitions for menthol that I've seen before include "mild analgesic" , "Chemical compound that smells like mint" , "Camphor used as a decongestant" , "medicinal compound" , "Peppermint camphor" .)