pile
$ \mathrm{pile}^1 |pīl|
/icons/point.icon meaning - "Stack" vs. "pile" vs. "heap" of paper - English Language & Usage Stack Exchange
If this is a lot to remember at once, you can think roughly of these terms as growing increasingly specific. RoaringFish's comment made me think of this ordering, which is by increasing messiness:
stack ≤ pile ≤ heap
You might also think of these as being proper inclusions if you are familiar with sets:
stack ⊂ pile ⊂ heap
/icons/point.icon 林　剛司（@Haya_Take）さん / Twitter
pile, stack, heapの違いは何となく感覚で使い分けていたがきちんと違いの説明を聞いて納得。｢書類の山｣を英語で何と言うか？角を揃えて整然と積み重ねてあればa stack of papers。雑然と、ならheap。とりあえず積んであればpile。
https://gyazo.com/12e8a6f17e0ed22a7af2195c2382f8b8
source: How to support diverse books as a blogger and reader - How-to
noun
a heap of things laid or lying one on top of another:
(同種の物の)山, 積み重ね (!整然と積み上げられた山; → heap)
e.g. he placed the books in a neat pile.
informal a large amount of something:
｟くだけて｠ ; 〖a ～/～s of A〗 たくさんのA〈物〉
e.g. the growing pile of work.
informal a lot of money:
｟くだけた話｠ ; 〖通例a/one's ～〗 大金, 財産
e.g. he is admired for having made a pile for himself.
a large imposing building or group of buildings:
｟主に英･おどけて｠ 大建築物(群)
e.g. a Victorian Gothic pile.
a series of plates of dissimilar metals laid one on another alternately to produce an electric current.
〘電〙 電池; 電堆（でんつい）
dated a nuclear reactor.
｟やや古｠ 〘物理〙 原子炉(atomic pile) (!現在では(nuclear) reactorが普通) .
archaic a funeral pyre.
｟古｠ (火葬用の)薪の山
verb
1. with object and adverbial place (things) one on top of another:
〈人が〉 «…に» 〈物など〉を積み上げる, 積み重ねる(up)(stack) «in, into, on, onto» ; 〖be ～d〗 〈物が〉積み上げられている, «…で» (表面が)覆われている «with»
e.g. she piled all the groceries on the counter.
(be piled with) be stacked or loaded with:
e.g. his in-box was piled high with papers.
(pile up) no object increase in quantity:
〈物が〉(集まって)山になる, 積もる, たまる(up)
e.g. the work has piled up.
(pile something up) cause to increase in quantity:
〈量〉を多くする; 〈仕事･問題など〉を抱えこむ, (山のように)ためる.
e.g. the debts he piled up.
(pile something on) informal intensify or exaggerate something for effect:
(急に)A〈体重など〉を増やす.; 〈感情など〉を必要以上に強く表す.
e.g. you can pile on the guilt but my heart has turned to stone.
2. no object (pile in/pile out) (of a group of people) get into or out of (a vehicle) in a disorganized manner:
pile in: ｟くだけて｠ 〈多くの人が〉A〈乗り物･場所〉に急いで乗り込む, どやどやと入る, どっと押し寄せる.
e.g. we all piled in and headed off to our mysterious destination
pile out: 〈多くの人が〉 【場所･乗り物などから】急いで降りる, どっと出る «of» .
e.g. my students piled out of three cars.
(pile into) (of a vehicle) crash into:
e.g. 60 cars piled into each other on I-95.
PHRASES
pile arms
see stack arms at stack.
pile it on
informal exaggerate the seriousness of a situation or of someone's behavior to increase guilt or distress.
make one's pile
informal make a lot of money.
ORIGIN
late Middle English: from Old French, from Latin pila ‘pillar, pier’.
$ \mathrm{pile}^2 |pīl|
noun
1. a heavy beam or post driven vertically into the bed of a river, soft ground, etc., to support the foundations of a structure.
〖～s〗 (建物や橋などを支える)杭（くい）, 支柱
2. Heraldry a triangular charge or ordinary formed by two lines meeting at an acute angle, usually pointing down from the top of the shield.
verb with object
strengthen or support (a structure) with piles.
〈物など〉に杭を打ち込む
ORIGIN
Old English pīl‘dart, arrow’, also ‘pointed stake’, of Germanic origin; related to Dutch pijl and German Pfeil, from Latin pilum ‘(heavy) javelin’.
$ \mathrm{pile}^3 |pīl|
noun
the soft projecting surface of a carpet or a fabric such as velvet or flannel, consisting of many small threads.
〖時にa ～〗 (カーペット･布･ベルベットの)けば, パイル(→ nap2)
verb with object, usually in combination (-piled)
furnish with a pile:
e.g. a thick-piled carpet.
ORIGIN
Middle English (in the sense ‘downy feather’): from Latin pilus ‘hair’. The current sense dates from the mid 16th century.