Teensy eensy tiny itty bitty little bit. All /e/ and /i/ front vowels. The mouth is literally closed up. Grand large vast ginormous expansive gargantuan. All /a/ back vowels. The mouth is literally relaxed and open. There are of course exceptions (big, small being notable) but English has a strong tendency in this way with size terms. Big = back and open vowel. Small = front and close vowel. This tendency isn't restricted to English; it shows up across languages in unrelated language families.
One of the classic linguistics experiments is Bouba and Kiki [1]. One of these shapes is called Bouba, and one is called Kiki. As you probably already instinctively know, the one on the right is Bouba, and the one on the left is Kiki. Arabic, Japanese, English, Swahili speakers all agree on this, with like 90% or greater concord across cultures being typical.
And one thing I noticed myself I haven't seen written about elsewhere. Take a look at the letter forms for how we write these sounds. In English: Bouba, Kiki. In Japanese: ボウバ and キキ. In Arabic: بوبا and كيكي. Bouba is written with round glyphs that enclose spaces. Kiki is written with sharp straight lines. Maybe that is just a coincidence. I haven't done a larger sampling than those three writing systems.
Other patterns tend to show up within a language, but not cross-linguistically, and are probably arbitrary associations formed simply because of existing patterns. For example with English:
* gl- : related to light -- glance, glare, glass, gleam, glimmer, glint, glisten, glitter, gloaming, gloom, gloss, glow
* sw- : related to a long movement - sway, sweep, swerve, swing, swipe, swirl, swoop, swoosh
The last three are very fun: swirl, swoop, swoosh. Swirl ends in -rl which literally curls (oh, there's that rl again) the tongue. A swoop ends with a stop consonant. Accordingly, it has more finality, suddenness, than swoosh. So: a bird swoops in to grab its prey. And a bird swooshes by, when it misses that prey.
[1] https://upload.wikimedia.org/wikipedia/commons/e/e7/Booba-Ki...
