Type Lambda λ on a Mac?

What is your reason for not wanting to switch the entire keyboard binding to Greek? If your reason was just that switching by the menu is a bit cumbersome, then you could set up a keyboard shortcut instead, for very quick layout switching.

With this, it takes just three keystrokes to type a λ (or any other Greek letter). I frequently need to type isolated Greek letters within a mostly latin-alphabet setting (I’m a mathematician), and I find this setup very convenient

In detail:

• Add a Greek keyboard layout to your input sources, under System Preferences > Keyboard > Input Sources:

• add a keyboard shortcut for switching to the most recently-used layout different from the current one, under System Preferences > Keyboard > Shortcuts > Input Sources. I use Command ⌘+Option ⌥+Space, which doesn’t (iirc) conflict with any system default shortcuts:

• Now you can get a λ by typing ⌘+⌥+Space (switch the input layout to Greek); l (actually produce the λ); ⌘+⌥+Space (switch back to whatever layout you were typing in before). And, as a bonus, the rest of the Greek alphabet is at your fingertips as well!

1. Press Command ⌘+Control ⌃+Space.
2. Type lamda into the search bar. Pay attention to type lamda instead of lambda.
3. Your lamda should be there:

You might ask why it is spelt lamda not lambda.

According to the link provided by MJeffryes:

The use of the spelling lamda derives from ISO 10646. This does not mean that it is more correct than lambda, merely that the spelling without the 'b' is the one used in the formal character names.

Here are two more links provided by Itai Ferber:

• Proof that lamda is in the standard
• Proof that lamda is in the standard since at least 1993

Here is a website about Mac keyboard shortcuts: https://support.apple.com/en-us/HT201236.

If you will be writing it often, I would recommend going to System Preferences → Keyboard → Text and adding a new replace rule: Replace lambda with λ.