source: [カービィがどんどん膨らんでっているGIF画像｜無料GIF画像検索 GIFMAGAZINE 64115]

the action of becoming larger or more extensive:

〖具体例ではan (...) ～/～s〗 【サイズ･範囲･量などの】膨張, 増大; 膨張量, 度 «of, in»

e.g. the rapid expansion of suburban Washington

e.g. a small expansion of industry.

extension of a state's territory by encroaching on that of other nations, pursued as a political strategy:

領土拡張

e.g. German expansion in the 1930s.

a thing formed by the enlargement, broadening, or development of something:

«…を» (以前よりも)発展させたもの «of, on, upon» ; (話題などの)展開, 広がり

e.g. the book is an expansion of a lecture given last year.

the increase in the volume of fuel on combustion in the cylinder of an engine, or the piston stroke in which this occurs.

〘機〙 (シリンダー内のガスの)膨張

early 17th century: from late Latin expansio(n-), from Latin expandere (see expand).