‘Slightly’ is an adverb and it means ‘to a small degree’ or ‘a little‘. The opposite meaning is ‘considerably’ = ‘to a large extent.’
The meaning is similar:
- The price is slightly higher.
- The price is a little higher.
‘slightly‘ adds more detail to ‘higher‘.
In the English Grammar Profile, B2 point 57 in the category of adjectives in the English Grammar Profile is defined:
‘SLIGHTLY’ to modify comparative adjectives to a small degree.
A search in the iWeb corpus:
1 SLIGHTLY HIGHER 29559
1 THAN (CSN ) 9879
2 PRICE (NN1 ) 1458
3 RATE (NN1 ) 1425
4 RATES (NN2 ) 702
5 RISK (NN1 ) 682
6 PRICES (NN2 ) 617
7 COST (NN1 ) 511
8 LEVELS (NN2 ) 409
9 INTEREST (NN1 ) 403
10 TEMPERATURE (NN1 ) 338
2 SLIGHTLY LARGER 22466
1 THAN (CSN ) 9478
2 SIZE (NN1 ) 1150
3 DIAMETER (NN1 ) 712
4 HOLE (NN1 ) 367
5 MALES (NN2 ) 359
3 SLIGHTLY SMALLER 15931
He can produce slightly smaller versions of himself. Each version can do only two things: radio information back to its parent, and produce slightly smaller versions of itself.