岩屋・石屋・窟|いわやiwaya[0]heiban (flat)

1. nouncavern; grotto

• Synonym洞穴ほらあなNeutralA general, everyday word for any cave, not limited to rock; 「岩屋」 refers specifically to a hole in rock and can also mean a dwelling carved into it.
• Synonym洞ほらNeutralA hollow in a cliff face or a large tree trunk, not necessarily in rock; 「岩屋」 is limited to holes in rock or dwellings carved from it.
• Synonym洞窟どうくつNeutralThe most common word for a deep cave in a cliff or rock, fitting any context; 「岩屋」 is used less often and has an old-fashioned flavor.
• Synonym岩窟がんくつWrittenA Sino-Japanese word for a cave in rock; its hard, stiff feel keeps it mostly to written prose, while 「洞窟」 is the usual everyday word.
• Synonym岩穴いわあなNeutralA cave in rock or a natural cave in the mountains, focusing on the hollow itself; 「岩屋」 can also mean a dwelling carved into rock.
• Synonym岩室いわむろWrittenA written word for a natural, room-like space in rock, stressing that the interior can shelter a person; rare in use, with 「洞窟」 the everyday choice.

For a cave in general, say 「洞窟」 or 「洞穴」. Use 「岩屋」 for a hole in rock or a dwelling carved from rock; 「岩窟」 suits written prose, 「洞」 fits hollows in trees or cliffs, and 「岩室」 is a rare written word for room-like rock spaces.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 岩いわに自然しぜんにできた洞穴ほらあな。
2. 岩いわに横穴よこあなを掘ほって作つくったすまい。