His expansiveness helped the new colleague adjust to the team quickly.

expansiveness 是由形容词 expansive（开朗的、热情的）加上名词后缀 -ness 构成的名词，表示"开朗热情的性格或态度"。expansive 本身来自动词 expand（扩展、展开），引申为"性格开朗、待人热情"的意思。