Legroom is the space in front of your seat. Not enough legroom, extra legroom, pay for legroom.
Airlines measure it as seat pitch, the distance from one seat back to the next, and it has fallen by several inches since the 1970s. Exit rows and bulkheads have the most, which is why they are sold separately.
1nounlegroomThe space in front of your seat.
“I always book an aisle seat because there's a bit more legroom.”
legroom is a space.
Leg plus room, from the plain description of the space needed.
From leg + room.
Etymology from Wiktionary, CC BY-SA