肆 sei³ {sì}

1. four (banker's anti-fraud numeral)
2. unrestrained
3. wanton
4. (literary) shop

肆行 si³ hang⁴ {sì xíng}

to act recklessly

肆意 si³ ji³ {sì yì}

1. wantonly
2. recklessly
3. willfully

肆虐 si³ joek⁶ {sì nüè}

1. to wreak havoc
2. to devastate

肆無忌憚〔-无-惮〕 si³ mou⁴ gei⁶ daan⁶ {sì wú jì dàn}

1. absolutely unrestrained
2. unbridled
3. without the slightest scruple