I was in Rona last night helping schlep around plywood that Rustin and his dad will use as sub-floor material. This sub-floor will (dis)appear under the much anticipated hardwood soon to grace the ground floor.
I was surprised to notice a product labelled ‘underlayment.’ It sounds conspicuously made-up. The Merriam-Webster defines it simply as ‘underlay.’ If it is just underlay, then the ‑ment suffix seems spurious and I question why the word is in the dictionary. See? This is why I don’t have a dictionary produced in the United States.
Uh oh. I just checked the Concise Oxford and ‘underlayment’ does not appear. To my surprise, it does appear in the Canadian Oxford. It’s a part of the definition for ‘underlay’ as a synonym. The dictionary labels ‘underlay’ as a verb and a noun while ‘underlayment’ is a noun. I blame the subversive American building product influence!
underlay¹ v. & n. • v.tr. (past and past part. -laid) lay something under (a thing) to support or raise it. • n. a thing laid under another, esp. material laid under a carpet or mattress as protection or support. underlayment n. [Old English underlecgan (as UNDER‑, LAY¹)]
Definition from the Canadian Oxford Dictionary.