Meaning of “swell” - Learner’s Dictionary

swell

verb uk us /swel/ (past tense swelled, past participle swollen, swelled)
SIZE [ I ] (also swell up)

to increase in size:

One side of his face had swollen up where he'd been stung.
AMOUNT [ I, T ]

to increase in amount because more things are added:

The population of the region was swollen by refugees from across the border.

(Definition of “swell verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)