Solution

ENGINE

4 clues

Diesel

Word class: Common noun
Nature of clue: Hint
Difficulty: Very easy
Sources: Boatload Puzzles
Topics: Technology, Vehicles - Transportation

Locomotive

Word class: Common noun
Nature of clue: Synonym
Difficulty: Easy
Sources: Boatload Puzzles
Topics: Vehicles - Transportation

Motor

Word class: Common noun
Nature of clue: Synonym
Difficulty: Very easy
Sources: Boatload Puzzles
Topics: Technology, Vehicles - Transportation

Power source

Word class: Common noun
Nature of clue: Description
Difficulty: Very easy
Sources: Boatload Puzzles
Topics: Technology

Other solutions to Power source

Words are categorized by artificial intelligence: there can be mistakes.