1.TTCthe amount of spaceabove your head, especially when you are in a car 〔尤指车辆中乘客头顶以上的〕头顶空间
2.TTRBritish EnglishBrE the amount of space above a vehicle when it is under a bridge 〔车顶与桥底之间的〕净空(高度)
Examples from the Corpus
headroom• Once fully open there is 25mheadroom above the river's 30m widenavigationchannel.• Legroom is generous, and headroom reasonably good.• Quantities of leg and headroom are generous, rearwardseattravel in particular, and all-roundvision is terrific.• The floor was often dug out by as much as three feet to increase headroom.• This gives the tape more headroom for high frequencies.• Paradoxically, my own company has always given plenty of headroom, but not everyone perceived it thus.• But once they're there, once you've given them headroom, they seem prettydetermined to stick around.