expression, i-adjective
Emphasizes extreme smallness; ごく is an adverb meaning 'very' or 'extremely'.
この部屋はごく小さいですが、居心地がいいです。
This room is very small, but it's comfortable.
ごく小さい頃からピアノを習っています。
I've been learning piano since I was very little.
とても小さい is a more common and neutral way to say 'very small'; ごく小さい sounds slightly more emphatic or literary.
極めて小さい is more formal and often used in written or technical contexts.
Combination of the adverb ごく (極, 'extremely') and the adjective 小さい ('small'). The adverb ごく is derived from the kanji 極 meaning 'extreme' or 'utmost'.