Find the missing elements

Question

In each of the groups below one or more words are missing. Can you figure out what the missing elements are? And what's the theme of each group?

Group 1
COMMANDMENT, PATCHWORK, LIGHTHEARTEDNESS, ?, DEFENSIVELY, DORSIFLEXION, PERSEVERANCE, ?, CONDITIONED, GENTLEMAN

Group 2
THRESHOLD, ORPHANAGE, ?, INGREDIENT, ABSOLUTELY, INDIGESTION, VIOLENTLY

Group 3
ANGLOPHILIA, UNBEATABLE, PROGRAMMABLE, DEVELOPMENTAL, ?, ZENITHAL, ACCEPTANCE, HYPOTHETICAL, IMPORTANT, ?, LAMBADA, ALUMINIUM, ALUMINIUM, ANXIOUS, ?, PRINCIPLE, COMPREHENSION, STIGMATIZE, ASTRONAUT, ?, ALPHABETICAL, MACHINE, COMPULSIVE, POMEGRANATE

Group 4
STRIKING, QUINTESSENCE, SKINTIGHT, OVERLOOK, ?, PRAISEWORTHINESS

Group 5
WRISTWATCH, COLUMNIST, ?, AGGREGATED, DUSTCLOTH, BENEVOLENTLY, PRESIDENT

Group 6
INEVITABLE, ENVIRONMENT, ?, NEVERTHELESS, EXQUISITE, DEVILFISH, ?, ELECTROTHERAPIST, SOMEWHAT, TENACIOUS

Answer 1

The words in the groups ...

... are the English names of items in closed sets such as the seven days of the week. They are padded to form other words. Conversely, each of the words in the question hides one of these words with all letters in order. For example ANGLOPHILIA hides ALPHA.

Group 1

TYPEFOUNDRY, EPIGRAPHIST — FOUR, EIGHT; the first ten English numbers

Group 2

PLAYFELLOWS — YELLOW; the seven colours of the rainbow.

Group 3

DEPHYSICALISATION, KAKORRAPHIAPHOBIA, SEISMOMICROPHONE, SUPERSTIMULATION — EPSILON, KAPPA, OMICRON and UPSILON; the 24 letters of the Greek alphabet.

Group 4

BISULPHOPHENYL — BISHOP; chess pieces

Group 5

GLUTATHIONYLATION — GLUTTONY; the seven deadly sins

Group 6

LITHOGRAPHIES, FRAUDPROOF — THGIE, RUOF; the first ten numbers in reverse order and written backwards

Choice of words

I don't think that there is a stricter criterion than just "contains the word", so I've just scoured a dictionary and used a word I liked and that disguises the hidden word reasonably well. I've tried to choose words that don't contain the "meat" verbatim, which turned out to be quite difficult for such common words as EIGHT and YELLOW.

The padding letters don't mean anything. UNBEATABLE leaves UNABLE after removing BETA, but other words don't have that property. Given how difficult it is to find words for KAPPA or GLUTTONY, that is no surprise.

It can't be a short word, because such words don't hide the "meat" very well. And, technically speaking, the shortest word that contains another word is that word itself. It also can't be the longest word, because if you use a bigger dictionary, you may come up with more such words, especially when you allow chemical terms. My dictionary finds

  PNEUMONOULTRAMICROSCOPICSILICOVOLCANOCONIOSES

as a word containing ONE with a signal-to-noise ratio of 1:14.

Uncommon words

An epigraphist studies epigraphs or inscriptions. In legal theory, dephysicalisation means that a physical thing in a property is replaced by an abstract right. Kakorraphiaphobia is the fear of failure, defeat or looking bad. The seismomicrophone was a listening apparatus to detect enemy activity in the galleries and trenches of WWI. Superstimulation is to cause an exeggerated or superstimulus. Bisulphophenly or disulphophenyl appears to be a compound used in chemical dyes. S-Glutathionylation is a modification of cysteine residues by the addition of glutathione.

Thanks to Techidiot for spotting the colours and the reversed numbers and thanks to Neil W for digging up glutathionylation!