the verb 'swell' originates from the old english 'swellan', meaning "to grow or make bigger, inflate". this old english term is derived from the proto-germanic 'swellaną', which carries the same sense of expansion or puffing up. this germanic root can be traced further back to the proto-indo-european root 'swel-', meaning "to swell", a root that also gave rise to words like 'sultry' through a different lineage involving the sense of being hot and swollen. the core concept of expansion and increase in size has remained remarkably consistent from its ancient origins to its modern meanings, which range from physical puffiness to the rising of the ocean and, informally, to a sense of excellence.

the word 'swell' is a simplex word of old english origin. it is not productively formed from smaller, independent morphemes in modern english.