also: はしご
In old documents, there are examples where 梯子 is read as ていし.
Using 梯子 read as ていし to mean stairs is almost never done in modern times.
Rare kanji spelling for はしご (ladder/stairs). The reading ていし is uncommon; the word is almost always written はしご in modern Japanese.
Standard modern spelling for ladder/stairs. The kanji form 梯子 is rarely used.
The kanji 梯 (ladder) and 子 (child/small thing) combine to form 梯子, originally meaning ladder. The reading ていし is the on'yomi, but the word is now almost exclusively read as はしご, the native Japanese reading.