Love a party with Royal Engineers (5)
I believe the answer is:
adore
'love' is the definition.
(adoring is a kind of loving)
'a party with royal engineers' is the wordplay.
'party' becomes 'do' (do can informally mean a party).
'with' means one lot of letters go next to another.
'royal engineers' becomes 'RE' (abbreviation).
'a'+'do'+'re'='ADORE'
(Other definitions for adore that I've seen before include "Worship, venerate" , "Cherish" , "Like a lot" , "Love greatly" , "Honour" .)