1To pile up or accumulate (intransitive); used for snow, dust, unfinished work, or feelings that build up over time.
昨夜の雪がまだ道路に厚く積もっている。
Last night's snow is still piled thickly on the road.
机の上に書類がどんどん積もっていく。
Papers keep piling up on my desk.
長年の不満が積もって、ついには口論になった。
Years of pent-up frustration finally led to an argument.
2To estimate or calculate an amount (transitive use). This is an old-fashioned use; in modern Japanese, 見積もる is used instead.
工事費はおよそ一千万円と積もられた。
The construction cost was estimated at around ten million yen.