Possible Clues:

• Small group nested inside larger group
• Circle within a circle, in a Venn diagram
• Minks, to weasels
• Part of mathematical collection that excites us best
• Naval craft prepared? Only a section
• Officers in crew, say, put on warship
• Group in a group
• Part of group setting British Standards in animal fat
• Ants, vis-a-vis insects
• Part of a larger group reversing vehicle on film stage