Britta gave him a conspiratorial smile.conspiratorialcon‧spi‧ra‧to‧ri‧al /kənˌspɪrəˈtɔːriəl/ adjective 
His voice became low and conspiratorial. Pat whispered to Maggie in a conspiratorial tone.conspiratorial whisper/smile/wink etc Britta gave him a conspiratorial smile.2relating to a conspiracy—conspiratorially adverb
EXAMPLES FROM THE CORPUS
- A friendly, conspiratorial smile for Bernice, a sympathetic glance for Defries, a half-angry, half-amused growl for Daak.
- Britta gave him a curiously conspiratorial smile.
- I don't want to make the novel sound wacky, let alone conspiratorial.
- Nick and I shot a conspiratorial look at each other: this time we would refuse to fight.
- The answers range from the technical to the vaguely conspiratorial.
- The behaviour of firms need not be conspiratorial in the legal sense.
- They were worn with one end thrown across the shoulder high under the chin, giving the wearer a conspiratorial air.
COLLOCATIONS FROM THE ENTRY Britta gave him a conspiratorial smile.COLLOCATIONS FROM OTHER ENTRIES
1a conspiratorial expression, voice, or manner suggests you are sharing a secret with someone: Britta gave him a conspiratorial smile. (=used when you share a secret with someone)· ‘Does she suspect anything?’ said Ruth in a conspiratorial whisper.
COLLOCATIONS FROM THE CORPUSNOUN· A friendly, conspiratorial smile for Bernice, a sympathetic glance for Defries, a half-angry, half-amused growl for Daak.· Britta gave him a curiously conspiratorial smile.
His voice became low and conspiratorial. Pat whispered to Maggie in a conspiratorial tone.conspiratorial whisper/smile/wink etc Britta gave him a conspiratorial smile.2relating to a conspiracy—conspiratorially adverb