speleology (also spelaeology)

n [U] 1 scientific study and exploration of caves 洞穴学. 2 sport of walking in and exploring caves 洞穴探险（运动）.

speechlessly, speechlessness, speed, speed limit, speed merchant, speed trap, speed up, speed-boat, speed-indicator, speed-up, speedboat, speedily, speediness, speeding, speedometer, speedway, speedwell, speedy, speleological (also spelaeological), speleologist (also spelaeologist), spell, spellbinder, spellbinding, spellbound, speller, spelling, spelt, spelunker, spend, spend...time (in) doing, spender, spending, spendthrift, spent, sperm, sperm whale, spermaceti, spermatozoon, spermicidal, spermicide,