As a noun, underlay is the thick soft material laid down on the floor first, before a carpet goes on top of it. You never see it once the carpet is down, but you feel it: it makes the carpet softer to walk on, quieter, warmer, and it makes the carpet last much longer. It is a normal shopping word in Britain, Australia and New Zealand — a carpet shop will ask what underlay you want.

As a noun當名詞用時, underlay is the thick soft material laid down on the floor firstunderlay是先鋪在地板上那層又厚又軟的材料, before a carpet goes on top of it然後地毯才鋪在它上面。You never see it once the carpet is down地毯鋪好之後你就看不到它了, but you feel it但你感覺得到它: it makes the carpet softer to walk on, quieter, warmer它讓地毯踩起來更軟、更安靜、更保暖, and it makes the carpet last much longer而且讓地毯用得更久。It is a normal shopping word in Britain, Australia and New Zealand在英國、澳洲和紐西蘭，這是購物時的常用字 — a carpet shop will ask what underlay you want地毯店會問你要哪種underlay。

American English much more often says 'padding' or 'carpet pad' for the same thing, so this is a word where the two Englishes genuinely part ways. It is usually uncountable ('we need more underlay'), though people do say 'a good underlay' when they mean a type.

American English much more often says 'padding' or 'carpet pad' for the same thing美式英文則更常把同樣的東西叫做『padding』或『carpet pad』, so this is a word where the two Englishes genuinely part ways所以這是一個英美用法真的分家的字。It is usually uncountable它通常是不可數名詞 ('we need more underlay')（『we need more underlay』）, though people do say 'a good underlay' when they mean a type不過如果是指某一種，大家也會說『a good underlay』。

There is also a verb 'underlay' (to lay something underneath), which is where the noun comes from, but the verb is rare and slightly technical, and it trips people up because its past tense is 'underlaid'.

There is also a verb 'underlay'另外還有一個動詞『underlay』 (to lay something underneath)（把某個東西鋪在下面）, which is where the noun comes from名詞就是從這裡來的, but the verb is rare and slightly technical但這個動詞很少見，而且有點專業, and it trips people up because its past tense is 'underlaid'而且會讓人搞混，因為它的過去式是『underlaid』。

The real trap is a different one, so watch out: 'underlay' also looks exactly like the past tense of the verb 'underlie' — 'the problems that underlay his decision' means 'that were underneath / behind his decision'. Same spelling, completely different word. Only the sentence tells you which one you are looking at.

The real trap is a different one, so watch out真正的陷阱是另一個，要小心: 'underlay' also looks exactly like the past tense of the verb 'underlie'『underlay』看起來也完全像動詞『underlie』的過去式 — 'the problems that underlay his decision'『the problems that underlay his decision』 means 'that were underneath / behind his decision'意思是『那些在他決定底下／背後的問題』。Same spelling拼法一樣, completely different word卻是完全不同的字。Only the sentence tells you which one you are looking at只有靠句子本身才能判斷你看到的是哪一個。