While both "extend" and "lengthen" suggest making something longer, there's a subtle but important difference. "Lengthen" specifically refers to increasing the length of something, usually a physical object. "Extend" has a broader meaning; it can refer to increasing length, but also to continuing something in time or space, or to making something apply to a larger area or group.

Let's look at some examples:

• Lengthen:

  • "I need to lengthen my skirt; it's too short." (Meaning: I need to make my skirt longer.)
  • "The days are lengthening as summer approaches." (Meaning: The days are getting longer in duration.)

• Extend:

  • "We're going to extend the kitchen by adding an extra room." (Meaning: We're going to make the kitchen longer.)
  • "The deadline has been extended to next week." (Meaning: The deadline has been moved to a later date.)
  • "I'd like to extend my thanks to everyone who helped." (Meaning: I'd like to express my gratitude to everyone who helped.)
  • "The shop has extended its opening hours during the holidays." (Meaning: The shop's operating time has increased.)

Notice how "extend" can refer to time, scope, or influence, in addition to physical length. This is the key difference. If you're talking strictly about making something physically longer, use "lengthen." If you're talking about increasing duration, range, or application, "extend" is often the better choice.

Happy learning!