部 bù is a pictophonetic compound: the right-side element 阝 (the city-mound radical, written 邑 yì when free-standing) carries the meaning, marking a settlement or an administrative division of territory, while the left-side element supplies the sound. When 阝 sits on the right of a character it almost always points to a place, a town, or a region under one authority; the same radical appears in 都 dū (capital city), 郡 jùn (commandery), and 邦 bāng (state). So at root 部 is a piece of land set under a single command, a district.

From that founding image of a marked-off division the modern senses fan out:

1. Part, section. A portion of a larger whole: 部分 bùfen (a part), 全部 quánbù (the whole of, every part), 局部 júbù (a local part).
2. Ministry, department, unit. A branch of an organization or army: 部门 bùmén (department), 部队 bùduì (military unit), 教育部 jiàoyùbù (the Ministry of Education).
3. Measure word. The classifier counted out for self-contained machines and works: 一部电影 yí bù diànyǐng (a film), 一部手机 yí bù shǒujī (a phone), 一部小说 yí bù xiǎoshuō (a novel).

The thread through every sense is division into bounded units. Whether the unit is a slice of a report, a wing of a government, a column of soldiers, or a single complete film, 部 frames it as one demarcated piece, the way the old city-mound framed one parcel of governed land.

The administrative root of 部 surfaces most plainly when it names a branch of an organization or army. A 部门 bùmén is a department, one demarcated wing of a company or institution. Scaled up to the level of the state, 部 is the formal word for a government ministry: 教育部 jiàoyùbù (the Ministry of Education), 外交部 wàijiāobù (the Ministry of Foreign Affairs), 财政部 cáizhèngbù (the Ministry of Finance). The pattern is fixed: a domain plus 部 gives the ministry that governs it.

The same logic runs through the military. A 部队 bùduì is a unit or formation of troops, a body of soldiers under one command, and 部 marks the column or detachment as a bounded fighting body. A senior officer commands his 部下 bùxià, the subordinates under him. Across civilian and military uses alike, 部 keeps its oldest sense: a piece of a larger whole, set apart and placed under a single authority.

Besides its noun life, 部 serves as a measure word, the classifier slotted between a number and certain nouns. It counts two families of things: large self-contained works and substantial machines. For works, 部 is the classifier for films, novels, dictionaries, and long compositions: 一部电影 yí bù diànyǐng (a film), 一部小说 yí bù xiǎoshuō (a novel), 一部词典 yí bù cídiǎn (a dictionary). For machines, it counts phones, cars, and pieces of equipment treated as complete units: 一部手机 yí bù shǒujī (a phone), 一部机器 yí bù jīqì (a machine).

The logic mirrors the noun. A 部-counted thing is a bounded whole made of many parts, a film of many scenes, a novel of many chapters, a machine of many components, complete in itself. For a single short film clip or a casual phone you will also hear the all-purpose 个 gè, but 部 is the formal, fitting classifier when the work or device is regarded as one finished, self-contained piece.

Picture the old city-mound on the right of 部, one parcel of land fenced off and placed under a single command. That bounded division is the whole character. Everything 部 means is a piece set apart as one unit.

Slice a thing and you have its 部分, a part; gather every slice and you have the 全部, the whole. Set apart a wing of an office and you have a 部门; set apart a body of troops and you have a 部队. And when you count out 一部电影 or 一部手机, you are tallying complete, self-contained units, a film whole in itself, a device whole in itself. Whenever you meet 部, look for the bounded unit, the parcel marked off from the rest.