1. 不定时的;不定期的
    If events or actions occur at irregular intervals, the periods of time between them are of different lengths.

irregular的解释

    e.g. Cars passed at irregular intervals...
           断断续续地有汽车驶过。
    e.g. She was taken to hospital suffering from an irregular heartbeat...
           她因心律不齐被送往医院。

2. 不规则的;不平整的;不直的
    Something that is irregular is not smooth or straight, or does not form a regular pattern.

    e.g. The paint was drying in irregular patches...
           油漆一片片地慢慢变干了。
    e.g. He had bad teeth, irregular and discolored.
           他牙齿长得不好，参差不齐而且有些发黄。

3. (行为)欺骗性的，不正当的,不合常规的
    Irregular behaviour is dishonest or not in accordance with the normal rules.

    e.g. ...the minister accused of irregular business practices...
           被控有违规商业行为的部长
    e.g. 'Will you do this for me, Leo? It's the only way.' — 'It's highly irregular, Ralph.'
           “利奥,你能为我做这件事吗？这是唯一的办法了。”——“拉尔夫,这么做是很不正当的。”

4. (动词、名词或形容词)不规则的
    An irregular verb, noun, or adjective has different forms from most other verbs, nouns, or adjectives in the language. For example, 'break' is an irregular verb because its past form is 'broke', not 'breaked'.

5. (部队)非正规的
    Irregular troops do not belong to an official national army.

    e.g. At least 17 different irregular units are engaged in the war.
           至少有 17 个非正规军部队参战。